An action verb is a word for the action of the subject. When the
object of a verb is a form of the subject or the subject becomes
the object, it is a linking verb.
Action verb: You appear before the committee tomorrow.
Linking verb: You appear tired.

Yes, the verb to appear can be a linking verb. A linking
verb acts as an equals sign, the direct object is another word for
the subject; for example, 'Mary is my sister.' (Mary=sister); or
the subject becomes the object, 'Mary's feet got wet.'
(feet-&gt;wet).
The fingerprints appear when the sunlight hits the glass.
(not a linking verb, no direct object)
The fingerprints appear the same as on the glass. (a
linking verb, fingerprints-&gt;same)
Some other verbs that can be linking verbs:
Appear
Seen
Become
Smell
Feel
Sound
Grow
Stay
look
Taste
Remain
Turn